﻿vi CONTENTS [volume lxi 



Undescribed plants from Guatemala and other 



Central American Republics. XXXIX - - John Donnell Smith 373 



Notes on the anatomy of the young tuber of Ipo- 



moea Batatas Lam. (with eight figures) - Florence A. McCormick 388 



Xerofotic movements in leaves (with eight figures) Frank C. Gates 309 



Physical properties of some toxic solutions 



George B. Rigg, H. L. Trumbull, and Mattie Lincoln 408 



Five undescribed species of Ravenelia - W.H.Long 417 



A study of the life history of Trillium cernuum L. 



(with plate XXVII) ------ Margaret Heatley 425 



The significance of color changes in oxidase re- 

 agents - - - - G.B. Reed 430 



Reduction divisions in the pollen mother cells of 

 Allium tricoccum. Contributions from the 

 Hull Botanical Laboratory 215 (with plates 



XXVIII-XXX and one figure) - - - - Mildred Nothnagel 453 

 The vegetation of the Selkirks (with map) - - Charles Hugh Shaw 477 

 Studies in the genus Bidens. III. Contributions 



from the Hulll Botanical Laboratory 216 (with 



plate XXXI) EarlE.Sherf 495 



The occurrence of bacteria in frozen soil (with two 



graphs) --------- B.C. Harder 507 



The prothallia of Ophioglossum vulgatum (with 



four figures) -------- Norma E. Pfeiffer 518 



The measurement of oxidation potential and its 



significance in the study of oxidases (with two 



figures) - - G.B. Reed 523 



Briefer Articles — 



Edward Lee Greene (with portrait) - - - - J.N. Rose 70 



The pollination of Asclepias cryptoceras (with one 



figure) ---------- Edwin Payson 72 



Physical conditions in sphagnum bogs - - - George B. Rigg 1 59 



Chloroform as a paraffin solvent in the imbedding 



process D.M. Mottier and W. J. G. Land 252 



Besseyosphaera, a new genus of the Volvocaceae - Walter R. Shaw 2 53 



A method for the dehydration of histological mate- 

 rial J. Ben Hill 255 



Bisporangiate cones of Larix (with one figure) - /. E. Kirkwood 256 



Preparation of copy 337 



